The present invention relates generally to the field of physical separation of materials and, in particular, to vibrating screens.
Vibrating screens are used by a number of industries, e.g., mining, food processing, sand-and-gravel, etc., to separate a fine portion of a heterogeneous substance from a coarse portion. For example, the mining industry (e.g., taconite processing) uses vibrating screens after the ore is crushed to separate fine ore from coarse ore. Typical screening processes involve placing a heterogeneous substance that comprises fine and coarse portions atop a screen. The screen is then vibrated so that the fine portion passes through the screen and the coarse portion stays atop the screen.
Typically, an electric motor having a rotating unbalance vibrates the screen. Electrical unbalance motors are usually heavy and bulky and normally require considerable maintenance and a heavy support structure. Another disadvantage is that such a configuration normally involves several moving parts, many of which are heavy and bulky, and a number of bearings. These moving parts and bearings require considerable maintenance and generate heat and excessive audible noise. Moreover, a substantial portion of the energy output of the electric motor typically goes into the useless elastic deformation of the heavy support structure and the generation of audible noise and heat.
To put this into perspective, the use of the above-type of vibrating screens during taconite processing will be used by way of example. Many of the screening operations used during taconite processing involve a motor vibrating a load that is at least 17 times the load of taconite to be screened. Moreover, the noise generated by the vibrating screens used in taconite processing may result in work environment safety issues. The taconite industry has identified vibrating screens as being responsible for substantial maintenance costs and production losses.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for vibrating screens that are smaller and lighter, that have fewer moving parts and fewer bearings, and that consequently are less noisy, require less maintenance, have reduced downtimes, and are more energy efficient than conventional vibrating screens.
The above-mentioned problems with conventional vibrating screens and other problems are addressed by embodiments of the present invention and will be understood by reading and studying the following specification. Embodiments of the present invention provide a screening machine.
More particularly, in one embodiment, a screening machine having a screen and a transducer that is substantially rigidly attached to the screen, where the transducer imparts a vibratory motion to the screen, is provided.
Another embodiment provides a screening machine that has a base and a screen that is coupled to the base to separate material by size. The screening machine also includes a vibration motor that has piezoelectric elements and a vibration amplifier located between the piezoelectric elements and the screen.
Another embodiment provides a screening method. The screening method includes transmitting an alternating voltage from a power supply to a transducer. The alternating voltage causes the transducer to produce a vibratory output. The method includes amplifying the vibratory output of the transducer by substantially rigidly attaching the transducer to a motion amplifier and vibrating a screen by imparting the amplified vibratory output to the screen by substantially rigidly attaching the motion amplifier to the screen. The method includes using a portion of the transducer as a sensor and transmitting a monitoring signal from the sensor to a control circuit that is indicative of the amplitude of the vibration of the screen. Also included is transmitting a control signal from the control circuit to the power supply and using the control signal to adjust the amplitude of the alternating voltage transmitted to the transducer and thereby the amplitude of the vibration of the screen.
Another embodiment provides a method for unclogging a screen. This method includes receiving a monitoring signal at a control circuit from a sensor that constitutes a portion of a transducer, where the transducer imparts a first vibratory motion to the screen as the result of a first alternating signal being transmitted to it from a signal-generator/amplifier and where the monitoring signal is indicative that the screen is clogged. The method includes evaluating the monitoring signal at the control circuit and transmitting a control signal to the signal-generator/amplifier, where the control signal causes the signal-generator/amplifier to superimpose a second alternating signal onto the first alternating signal. Also included is transmitting the superimposed first and second alternating signals to the transducer that imparts a vibratory motion to the screen. This vibratory motion includes a superposition of first and second vibratory motions as a result of the superimposed first and second alternating signals.